Edit: Ignore this post! I just realized it was already mentioned somewhere in Barddas' "Celtic Tribes Re-visited" post.

I was looking at a map of Free Gaul before the invasion of the Romans. (Free Gaul was what is now France.) There were labels of where some of the Celtic tribes lived and when I saw one of them named "Parisii" (or Parisi or something), I went to an atlas and right where the tribe was labelled on the Gaul map, the city of Paris was located on the modern map!